System of control.



L. G. RILEY.

SYSTEM OF CONTROL.

APPLICATION FILED APR. 2a. 1915.

1,293,929. Patented Feb. 11,1919.

plum/g g1 INVENTOR m7 6. PM;

film/0X0 4 A ATTORNFY WLTNESSES term on the above-indicated UNITEDSTATES PATENT ornron.

LYNN G. RILEY, OF WILKINSBUBG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSEELECTRIC. AND MANUFACTURING COMPANY, A CORPORATION OF SYLVAN IA.

SYSTEM OF CONTROL.

Specification of Letters Patent.

Patented Feb. 11, 1919.

Application filed April 23, 1915. Serial No. 233%15.

To all whom it may concern:

Be it known that I, LYNN G. RILEY, a citizen of the United States, anda-resident of Wilkinsburg, in the'county of Allegheny and State ofPennsylvania, have invented a new and usefullmprovement in Systems ofControl, of which the following is a specification.

My invention relates to systems of control, and it has'special referenceto the automatic-series-parallel control of electric railway vehiclemotors and the like.

One of the objects of my invention is to provide a relatively simple andreliable syscharacter for preventing undesirable rushes of current andtoo sudden acceleration of a vehicle during a predetermined portion ofits accelerating period.

Another object of my invention is to provide a simple auxiliary meansfor use in connection with a line relay device for permitting theoperation of certain switches to set up dynamic braking of vehiclemotors upon an interruption of supply-circuit volta e.

l tnotherobject of my invention is to provide an improved type ofbridging transition from series to parallel relation of the motors,whereby the acceleration during such transition may be effected morerapidly and smoothly than heretofore.

In the prior art, when employing the field-control vehicle motors, ithas been customary to simultaneously exclude predetermined portions ofthe field windings of the respective motors from circuit, therebycausing undesirable rushes of current and too sudden acceleration' ofthe vehicle. I'- provide automatic means for effecting the change fromfull to normal field strength of the respective motors successively,thus preventing the undesirable conditions referred to. Moreover, whenthe supply-circuit voltage has temporarily failed so that the line relayswitch has dropped to open the customary circuits, it has beenimpossible to actuate the motor-controlling switches to set up dynamicbraking and retard the movement of the vehicle. My present systemprovides simple meansto be actuated by the train operator to allow theaction of such sistors R1 and R2 and type of system for electricswitches in an emergency, whereby the vehicle speed may be controlled,as more fully set forth hereinafter.

In the accompanying drawing, Figure 1 is a diagrammatic view of the maincircuits of a system of control embodying my invention; Fig. 2 is adiagrammatic view of the auxiliary governing circuits for the systemshown in Fig. 1; Fig.3 is a sequence chart of well known form forindicating the sequence of operation of the various switching devicesthat are illustrated in Fig. 1; and Fig. 4: is a complete diagrammaticview of one of the switching devices.

Referring to Fig. l of the drawing, the system here shown comprises apair of suitable supply-circuit conductors respectively marked Trolleyand Ground; a plurality of electric motors respectively having armaturesA1 and A2 and subdivided field windings F1 and F 2, to permit of fieldcontrol of the motors; a reversing switch RS, preferably ofthe familiarelectrically-colitrolled drum type, for simultaneously reversing theelectrical relations of the respective armatures and field windings; a

plurality of motor-controlling switches LS1,

LS2, M2, JR, J, and G of a familiar electrically-controlled type; amechanically-actuated switching apparatus PK, preferably of the drumtype, that is employed in connection with a plurality of acceleratingrealso for varying the active amounts of thefield windings duringacceleration; and another accelerating resistor AR that is adapted to beshort-circuited' by the closure of the switches LS1 and LS2. The systemis also provided with a limit switch L that is connected in circuit in amanner to be described, and an overload trip switch OT of a familiartype.

' The apparatus PK is adapted to assume a plurality of operativepositions 1 to 7, inclusive, and comprises a plurality of alined controldrums Dland D2 that are respectively provided with. operating shafts 1and 2 upon which is mounted a centrally located pinion 3 that is adaptedto mesh with a suitable rack member 4. A plurality of suitable pistons 5and 6 are respectively secured to the ends of the rack member 4 and aredisposed to operate within suitable cylinders 7 and 8, respectively. Asuitable valve mem'ber'9- is adapted, when actuated,'to admitfluid-pressure from any suitable source (not shown) to the cylinder 7,and a second. valve member 10 is normally adapted to admit fluidpressure to the cylinder 8. The valve members 9 and 10 are also adaptedto be electrically controlled, through the agency of suitable coils 11and 12, respectively, that are connected in the auxiliary system shownin Fig. 2, as hereinafter set forth.

The operation of the apparatus PK may be described as follows: In theposition shown in the drawing, with both the magnet coils 11 and 12denergized, fluid pressure is admitted through the valve member 10 tothe cylinder 8 to drums D1 and D2 to the position shown in the drawing,which corresponds to the OE position of the master controller that isillustrated in Fig. 2. To effect movement of the drums D1 and-D2 themagnet coils 11 and 12 are energized, whereuponfluid pressure isadmitted through the valvemember 9 to the cylinder 7 and is exhaustedfrom the cylinder 8 through the valve member 10,

thereby rotating the control drums through their successive operativepositions. The general arrangement of parts, including the size of thevalve openings and the customarily-provided drum star wheel device (notshown), is such. that the apparatus PK is adapted to stop only in itsdefinite positions, 1 to 7, inclusive, as will be understood. To arrestthe movement of the drums in any position, it is merely necessary todenergize the magnet coil 12, whereupon the valve opens to admit fluidpressure to the cylinder 8 and to balance the pressure in the cylinder7, thereby maintaining the control drums D1 and D2 in the desiredposition until the magnet coil' 12 is again energized. Where the magnetcoil 12 is intermittently energized through the agency of the limitswitch L in accordance with the value of the accelerating current, asset forth later, the control drums are given a step-by-step movement togradually exclude from circuit the accelerating resistors R1 and R2 andto subsequently vary the active amounts of the field windings F1 and F2.To return the control drums D1 and D2 to the first position shown in thedrawing, it is merely necessary to denergize both magnet coils 11 and12, whereupon fluid pressure is admitted to the cylinder 8 and isexhausted from the cylinder 7;

The limit switch L is provided with the customary series coil 13 that ishere connect ed in series circuit with the armature A2 and is alsoprovided with an auxiliary shuntconnected, difl'erentially-wound coil 14that is energized in the manner to be described in connection with thesystem shown in Fig; 2. The usual auxiliary contact members 15 foropening and closing circuits of and without regard to bias the piston 6and the;

contact segment of the switches M2 the auxiliary governing system arealso as-. sociated withthe limit switch. v The general operation of thesystem, so far as the main circuits of Fig. 1 are concerned theparticular auxil iary governing systemthat is illustrated in Fig. 2, maybe set forth as follows. Energy is first supplied from the trolleyconductor, through the switch LS1, the accelerating resistor AR, thearmature A1, suitable contact members of the reversing switch RS, thefull field winding F1, control fingers 16 and 17 that are bridged by.contact segment 18 of the control drum D1, other contact members of thereversing switch RS, the accelerating resistor R1, the switch J R, theac celerating resistor switch RS, the full field windingF2,'controlfingers 19 21 of the control drum D2, again through thereversing switch RS and the actuating coils 13 of the limitswitch L tothe negative conductor.

As indicated by the sequence chart of Fig. 3', the switch LS2 is nextclosed to shortcircuit the accelerating resistor AR and the apparatus PKis then gradually moved, in the step-by-step manner scribed, togradually short-circuit the resist ors R1 and R2: In-position 2 of thecontrol drums, a contact segment 22 engages control fingers 23 and 24;to short-circuit one section of the resistor R1; in position 3, acontact segment 26 and 27 to exclude a sistor R2ffrom circuit; inpositionv 4, control finger 28 engages contact the control drum D1 tocomplete the shortgircuit of the resistor R1; while, in position 7 ment25 of the drum D2 to complete the exclusion from circuit of the resistorR2.

The transition of the motors from series to parallel relation is. theneffected by the initial closure of the switch J, the quent opening ofthe switch JR and the concurrent return of the drumsDl and D2 to theirinitial position 1, and the final closure and G accompanied by theopeningof the switch J, as hereinafter set forth in detail, inconnection with Fig. 2. The apparatus PK is then actuated through itsfirst five positions, in a manner similar to that already described.

When drums-D1 and position 6, control finger 32 engages contact segment33 and control finger 16 is disengaged from contact segment 18, wherebya predetermined portion of the field winding F1 is excluded from circuitto produce further acceleration of the corresponding motor, inaccordance with familiar practice. As soon as the control drums D1 andD2 occupy their final position 7, a control finger and 20 that arebridged by.

25 bridges control fingers portion ofthe resegment 29 of a controlfinger 30 engages contact seg-' R2, the armature A2, other contactmembers of the reversing subse D2 are actuated to 34 engages contactsegment 35 of the drum D2, while control finger 19 breaks contact withthe contact segment 21 thereof, thereby reducing the full field windingto normal field Winding connection in the other motor, in the samemanner as that described I in connection with the field winding F1. Itwill be observed that the resistors R1 and R2 are gradually excludedfrom circuit in corresponding successive steps and that the activeamounts of the field windings F1 and F2 are also varied successively andcontrollably in accordance with the value of legends employed, as morefully illustrated in Fig. 4; a master controller MC and a masterreverser MB for supplyingenerg'y ward, olf and reverse to the variousactuating coils from a suitable source of energy, plurality oftrain-line conductors TL and a line relay switch LR of a familiar type.The master controller MC is adapted-to assume a plurality of operativeositions, a, b. and 0, respectively correspon ing to initial-series,full-series, and full-parallel relation of the motors, shown beingautomatic, the controller may be directly thrown to its final positiona, as will be understood. The master reverser MR isadapted to assume thecustomaryforpositions, and is provided with suitable correspondingcontact members, as hereinafter described.

The line relay switch LR is shown as provided with an actuating coil 36,the respective ends of which are adapted to,be connected to the supplycircuit conductors Trolley and Ground, as indicated in Fig. 2. Theswitch is adapted to occupy a lower position, when the coil 36 isdenergized, for completing certain auxiliary circuits, and an upperposition when the coil 36 is energized to complete other auxiliarycircuits, as hereinafter more fully set forth.

The shunt coil 14 of the limit switch L is shown .as energized from thebattery B I through the master controllers, and a contact segment 37 ofthe drum D2, and its energizing effect upon the limit switch op-' posesthe action of the'series'coil 13 and may be varied in accordance withpredetermined conditions by means ofasuitable variable resistor 38. Theparticular means for varyingthe resistor 38 of this control device,however, forms no essential part of my scrlbed Francis such as a batteryB; a

'versing switch RS, conductor 64,

However, the system,

present invention and is fully shown and dein a co-pending applicationof H. Shepard,Serial No. 785, filed January 6, 1915, and assigned to theWestinghouse Electric and Mfg. Company.

Assuming the master reverser MR to be moved to its forward position andthe master controller MC to be actuated to its final running position 0,the automatic operation of the auxiliary control system may be 75describedas follows: A circuit is first established from one terminal ofthe battery B through conductor 40, train line conductor 41, conductor42, control fingers 43 and 44 that are bridged by contact segment 45 ofposition, conductor 46, control fingers 47 and 48 that are bridged bycontact segment 49 of the master controller in its positions a, b and 0,conductors 50 and 51, coiiperating contact members 51 of the overloadtrip OT, conductor 52, electrical. interlock 53 J- out, conductor 54,interlock M2out, the actuatingcoil of the switch JR, conductors 55 and56, train-line conductor 57, conductor 58, control fingers 59 and 60thatare bridged by contact segment 61 in the forward position of the masterreverser MR, and thence to thenegative conducton,

Another circuit is simultaneously established from train-line conductor41, through conductor 62, contact segment 63 of the recotiperatingcontact members 64*.of the overload trip OT in its closed position,contact seg ment 65drum1 that is adapted to complete the circuit inquestion when the apparatus PK occupies its initial position 1,conductor 65, actuating coil of the switch LS1,

conductor 66, coiiperating stationary and movable contact members 67 ofthe line relay switch LR in its upper position, and thence throughconductor 56 to the negative conductor in the :manner already described.

As soon, as the switch LS1 has closed, an interlock LS1in bridges thecontact segment 65drum1, thereby insuring the closure-of the switch LS1throughout the subsequent operation of the system, irrespective of theposition of the control drums D1 and D2.

Another circuit is then established from conductor 65 through conductor68, interlock Jout and'the magnet coil 11 of the apparatus PK to thenegative conductor through conductor 66 and the line relay switchcontact members 67, as hereinbefore mentioned. A further circuit isestablished from energized contact segment 69 of the master controllerMC in its positions I) andconductor 76, cooperating contact members 15of the limit switch L, provided the limit switch has. dropped to itslower position, conductor 77, interlock 78-LS2out,' the 6 actuating coilofthe switch'LS2, interlock LSl-in' and the negative-connected conductor55. As soon as the switch LS2 has closed to short-circuit theaccelerating resistor AR, the energizing circuit for its actuating coilistransferred through interlock 78 and conductor 7 8 to the conductor68.

The closure of the switchLS2 causes the establishment of another controlcircuit from conductor 77, as soon as the limit switch L has againdropped to its lower position, through interlock 7 9-LS2-in, conductor80, interlock Jout, and the magnet coil 12 of the apparatus PK to thenegative-connect'ed conductor66. The two magnet coils 11 and 12 of theapparatus PK being thus energized, the control drums D1 and D2 will moveforward in a step-by-step manner, in accordance with the position of thelimit switch L, to'gradually effect the short-circuiting of theresistors R1 and R2, as hereinbefore described.

After the drums leave position 4, the contact segment 37 of drum D2breaks the connection between conductors 72 and-73, thus denergizing themagnet coil 12 of the drums, irrespective of the position of the I limitswitch L. In this way, the drums are prevented from passing beyondposition 5 while the interlock 75 of the switch J R oc-' cupies its inposition, or, in other words, while the motors are connected in seriesrelation.

Assoon as the apparatus PK has reached 1 its finalresistor-short-circuiting position 5, anothercircuit is established froman energizing contact segment 81 in position 0 of the master controllerthrough control finger 82, conductors'83 and 83 contact segment 84: ofthe control drum D1 in any of its positions 5 to 7, inclusive, conductor85, interlock Gout to the actuating coil of the switch J and thenegative-connected conductor 55.

As soon as the switch J is closed, the switch JR is opened by reasonofthe exclusion from its control circuit of the interlock 53J-out, and themagnet coil 11 of the apparatus PK is simultaneously denergized bycontrol circuit of the corresponding interlock Jout., The magnet coil 12being deenergized, as already pointed out, the control drums D1 and D2are returned to their initial position 1 by reason of the concurrent denergization of the magnet coils 11 and 12, as hereinbefore explained.

Provided the limit switch L occupies its lower position, a circuit isnext established from conductor 77, through interlock 6a 79-LS2-in,conductor 86, interlock 87 The closure of the switch M2 closes a holdandR2, while the limit switch L is being position,-the switches M2 and Gcan be imreason of the exclusion from its naeaeae drum 1,interlock 87-M2-out, conductor 87 interlock JR-out, the parallel-connected actuatingcoils of the switches M2 and G, and; conductor 55 to the negativeconductor.

ing circuit therefor from conductor 87*, through interlock 87 a andconductor 87 to the conductor 52.

Whereas, in the usual type of bridging series-parallel control, the Jswitch is closed in accordance with the position of a limit.

switch after the various accelerating resistors havebeen completelyshort-circuited,

' and the initial short-circuits of the resistors are thereafter removedto render them adapt- '80 able for subsequent service in connectionwiththe parallel operation of the motors, and the switches M2 and G arefinally brought in to complete the initial parallel connection of themotors,-it will be observed that, in the bridging transition justdescribed, the J switch is closed to substitute for the initialshort-circuits of both resistors R1 and R2, irrespective of the limitswitch L, as soon as the accelerating resistors have been initiallycompletely short-circuited, and the control drums D1 and D2 arereturnedto their initial position 1 to remove the initial short-circuitsfrom the resistors R1 held in its upper position by the flow of currentincident to the final short-circuit of the accelerating resistors.Consequently, as soon as the limit switch drops to its lower mediatelyclosed in the manner just recited to directly dispose the motors ininitial parallel relation, andthetransition of the motors from-series toparallel relation is accomplished more rapidly than heretofore and witha more continuous and uniform load upon the motors, thereby providing asmooth and more satisfactory operation of the motors during thetransition period.

As soon as the switch J has been'opened, by reasonof the exclusion fromits control circuit of the interlock Gout upon the closure of theswitch'G, and provided the limit switch L occupies its lower position, 1the energizlng circuit of the actuating coil below, to graduallyshort-circuit the accelerating resistorsRl and R2, until the posi- 126tion 5 is reached.

The action of the drums D1 and D2 is somewhat different during parallelmotor operatlon from the action during series operation, by reason ofthe fact that the series 130 so that the limit switch actuating cil 13of the limit switch L is adapted to receive the current from thearmature A2 only. During series operation, the same current traversesboth armatures, lifts to temporarily arrest the movement of the drumswhenever a section of either the resistor R1 or the resistor R2 isshort-circuited. The drums move forward, therefore, one step at a time.On the other hand, during parallel motor operation, the limit switchlifts only when the current traversing the armature A2 exceeds apredetermined value. The drums thus move forward two steps'betweenstops, as indicated in the sequence chart, inasmuch as the currenttraversing the armature A1 does not influence the limit switch coil.However, the movement of the drum between stops is not too rapid topermit the active amounts of the field windings F1 and F2 to be varied.successively in drum positions 6 and 7 to thus partially reduce the rushof current, as described in connection with Fig. 1.

In order to further reduce the accelerating current duringfield-changing conditions, the shunt-connected switch L is renderedinoperative by reason of the contact segment 37 of the drum D2 againbreaking the connection between conductors 72 and 7 3 after the-drumsleave position 4. In this case, however, the magnet coil 12 of the drumsis not deenergized, by reason of the interlock 75 of the switchoccupying its in position, as already mentioned.

Since the actuating coils 13 and 14 of the limit switch L are adapted,when energized, to oppositely or difi'erentially influence the switch,it follows that, with the coil 14 excluded from circuit, the effect ofthe series coil 13 will be strengthened, or, in other words, the limitswitch will lift at a relatively low value of accelerating current afterthe drums D1 and D2 occupy position 5, thereby further preventingundeslrable current peaks during field-changing conditions.

When the control drums D1 and D2 occupy their final operating position7, the

two motors are disposed in full parallel relation with normal fieldstrength in each motor.

The emergency operation of the line relay switch LR will now bedescribed: If the supply-circuit voltage fails, or if, for any otherreason, the switch LR drops to its lower position, the energizingcircuits of the various actuating coils that are connected to theconductor 66 are broken at the switch by reason of the interruption ofthe connection between conductors 66 and 56. If it is desired to operatecertain of the motor-controlling switches to effect dynamic braking ofthe motors under emergency conditions, an auxiliary switching device or67 of the the negative conductor.

coil 14 of the limit push-button PB, that is preferably located near themaster controller, may be actuated by the train operator, may becompleted from the actuating coils of the switches to be actuatedthrough condnctor 66, the cooperating contact members line relay switchLR in its new or lower position, conductor 88, train-line conductor 88*,conductor 89, the push-button PB in its operative position, conductor90, control fingers 91 and 60 that are bridged by the contact segment 61in the forward position of the master reverser, and thence to Upon theconcurrent operation of the push-button PB and the master controller MC,therefore, the actuating coils of the various motor-controllingswitches, that are connected to the conductors 66, may be energized andthe switches may be operated to set up dynamic braking through theclosed "motor circuit, with the line relay switch occupying its lower oremergency position, as will be understood. i

I do not wish to 'be restricted to the specific circuit connections orarrangement of parts herein set forth, as various modifications of myinvention may be made without departing from the spirit and scopethereof. I desire, therefore, that only such limitatlons shall beimposed as are indicated in the appended clalms.

I claim as my invention:

' 1. In a system of control, the combination with a plurality ofelectric motors severally having armatures and field magnet windlngs, ofmeans for connecting said motors in various circuit relations, aplurality of accelerating resistors, a control drum comprising contactmeans for gradually excluding said resistors from circuit and othercontact means for successively varying the active portions of the fieldwinding to effect acceleration of the motors, when the latter areconnected in various circuit relations, and means actuated in accordancewith the accelerating current for automatically operating said drum fromits initial to its final position in a step-by-step manner.

2. In a system of control, the combination with a lurality of electricmotors severally havin armatures and subdivided field-magnet w ndings,of means for connecting said motors in series and in parallel relation,a plurality of accelerating resistors, a multi-position control drum,and automatic means governed by the current flowing through the motorsfor operating said control drum in a forward direction to gradually,exclude the resistors from circuit when the motors are in seriesrelation, for returning the control drum to initial position and foroperating the drum again in a forward direction to successively excludeportions of said resistors and portions of whereupon a circuit saidfieldwindings from circuit when the motors are connected in parallel relation3. In a system of control, the combination with an electric motor, and aplurality of controlling devices therefor, of a switching deviceadapted, under normal conditions, to

permit the actuation of a predetermined number of said controllingdevices. and adapted, under predetermined conditions, to prevent theactuation of certain controlling devices, and auxiliary means forrendering said switching device again fully operative under otherpredetermined conditions.

ii. In a system of control, the combination with a supply circuit, anelectric motor, and a plurality of controlling devices thereforseverally provided with actuating coils, of

- a switching device adapted, in its normal posltion, to permit.energization' of certain actuating coils and adapted to assume a newposition to prevent the energization of said certain coils upon aninterruption of the supply-circuit voltage, and auxiliary manual-operable means adapted to thereupon permit a reenergization of saidcertain coils.

5. In a system of control, the combination with a supply circuit, anelectric motor, and a plural ty of controlling devices. thereforseverally provided with actuating coils, of

an auxiliary source of energy, a relay device adapted, while energizedfrom said supply c1rcu1t, to complete an energizing circuit 1 from saidauxiliary source for certain actuating coils and adapted to assume a newposition to open the energizing circuit of said certain actuatin ruptionof the supp y-circuit voltage, and auxiliary manually-operable switchingmeans 7 for re-completing said last energizing circuits through the newposition of said relay device.

' 6. In an automatic series-parallel system of control, the combinationwith a plurality of electric motors and 'a plurality of ac- 1 subsequentservice, means dependent upon celerating resistors, ofmeans forigraduall excluding sald resistors from c1rcu1t to e feet accelerationof said motors to full series relation, a switching device adapted to bethereupon substituted for said resistor-excludlng means to adapt theresistors for predetermined conditions for thereupon directly disposingthe motors in parallel relation, with said resistors in the respectivemotor circuits, and means for again efiecting the exclusion fromcircuitof said resistors to accelerate the motors to full parallelrelation.

of control, the combination with a plurality of electric motors and aplurality of accelerating resistors, of a control drum adapted to bemoved through successive positions in accordance with theacceleratinoperative. coils upon an inter 7 In an automaticseries-parallel system' ing current to exclude said resistors fromcircuit to effect acceleration of said motors fecting the operation ofsaid drum to accelerate the motors to full parallel relation.- 8. In asystem'of control, the combinat on with an electric motor, of amulti-posltion controlling device adapted to efiect motor acceleration,a. switching device provided with a plurality of actuating coils andadapted, under predetermined conditions, to govern the operation of saidcontrolling device, and means dependent upon the positionofthe'controlling device for rendering one of said coilsoperative orinoperative.

9. Ina system of control, the combination with an electric motor, of amulti-position controller adapted to efiect motor acceleration, a limitswitch provided with a plurality of actuating coils energizedfromdifferent sources and adapted to govern said controller inaccordance with accelerating current conditions, and contact meansdependent upon the position of theoontroller for rendering 10. In asystem of control, the combination with an electric motor, of amulti-positioncontroller adapted to effect motor acceleration, a limitswitch providediwith a plurality of difierentially-energized actuatingcoils and adapted to govern said con-.

troller in accordance with accelerating current conditions, and contactmeans for rendering one of said coils inoperative in certain controllerpositions to thereby cause said limit switch to operate at a relativelylow current value.

11. In a system of control, the combination with an electric motorhaving an armature and a sub-divided field magnet winding, ofanaccelerating resistor, a multiposition controller adapted to graduallyshort-circuit said resistor and to subseone of said coils operative or,

quently vary the active amount of said field winding, an auxiliarysource ofenergy, a limit switch providedwith a plurality ofdifferentially-disposed actuating coils respectively energized from themotor current and said auxiliary source and adapted to govern theoperation of said controller in accordance with accelerating currentconditions, and contact means for rendering the auxiliary-sourceenergized coil inoperative when sald resistor is short-circuited,

whereby the motor current during fieldchanging conditions ismaintainedat a relatively low average value.

12. In a series-parallel system of control, the combination with asupply circuit, and a plurality of electric motors severally havingarmatures and subdivided field-magnet windings, of a plurality ofaccelerating resistors, a multi-position accelerating controller, aplurality of actuating coils therefor, an auxiliary source of energy, alimit switch provided with a pair of difieren- I 'tially-dlsposedactuating coils respectively energized from the motor current and saidauxiliary source and adapted to govern the operation of said controllerin accordance with accelerating current conditions, means for initiallyenergizing the controller-actuating coils to effect the gradualshort-circuit of said resistors with the motors in series relation,means including contact means ,on said controller for effecting thereturn of the controller to its initial position during transition ofthe motors toparallel relation,

means for again effecting the short-circuit of said resistors,

and means for then employing said contact means to render theauxiliarysource-energized coil of the limit switch inpredeterminedportions of the field windings from circuit, whereby the motor currentduring field-changing conditions is maintained at 'a relatively lowaverage value. 13. In a system of control, the combination with a supplycircuit, a plurality of motors having armature and field rwindings, aplurality of resistors in the circuit of said motors and a drumcontroller, of means for connecting said motors in series and inparallel relation across the supply circuit, and means governed by thecurrent flowing through the motors for effecting a continuous automaticaction, including operating said controller to gradually exclude saidresistors from circuit when the motorsare in series relation, effectingtransition of the motors, and excluding said resistors and a portion ofsaid field windings when the motors are in parallel relation.

In testimony whereof, I have hereunto subscribed my name this 19th dayof April LYNN G. RILEY.

